Repointing - Oh God I am confused

[thiambal]

Hi all,

I have read through old topic on repointing and quite frankly I am more confused than when I started.

I have got to re-point the front garden wall. It is only 5-6 bricks high so not a big job. Although there is a one brick pillar/pier which has almost no mortar in it at all and may need rebuilding. The wall has been partly repointed before by a previous owner using what looks like cement mortar. This has had no ill-effects on the bricks but the pointing was only 3-4mm deep so it has mostly fallen out. What lays behind this pointing I assume is original and appears to be just sand in look and consistency.

At some point in the future I am going to re-instate a brick pillar/pier at the end of this wall but will be using a suitable style modern brick as I just cannot afford re-claimed. Ideally then I want to use the same mix for the pointing and the new brick work.

So the question is what mix do I use for the repointing? I would also add that I am a cack-handed fool and the little bit of pointing I have done in the past with a pre-mixed lime mortar looks awful because the surrounding bricks have white stains and the mortar itself is bright white and quite out of keeping with the property. I therefore deeply fear the use of the bright white stuff. What ever mix I use I want to colour it to blend in. Can people suggest the best way to consitently colout mortar?

Right, over to you chaps and chapesses.

Sam

 

[Jon Maine]

Firstly I would use a hydraulic lime NHL3.5 to do that job. When you mix the mortar it needs to be 3 parts aggregate to one part lime.

Look at the different colours of aggregate that are locally available, you can also use ash to colour a mix to. Best just experiment with some different combinations of aggregate to get different results. There are many lime merchants on the internet who supply different aggregates although a trip around the local builders merchants may help.

You need to guage your mortar by volume, using a suitable container filled to the brim and levelled off. When you get the colour you want after experimenting write down the recipe and where you got the materials so you can reproduce it again in the future.

If you hold a flat board or slate level with the top of the lower brick with your mortar not to wet so it holds together but is not runny, flattened into a pancake the height of the joint just cut off a sausage of mortar the depth of the joint and gently slide it into the joint with your trowel tipped backwards slightly. Push hard with a twist of the wrist tipping the trowel backwards at the top you should manage with a little practice not to smear the the face of the bricks. The vertical joints "perps" are not so easy for a novice but again if you get a sausage the right length and girth to fill the joint you should with the correct flick of your wrist be able to push it into the joint again without smearing the surface of the brick.

Good luck

 

[Nemesis]

I once watched a TV prog where somewhere important (Chatsworth maybe) was being repointed with lime - very narrow joints. The bloke doing it had put masking tape each side of the joints in order to try to avoid the smearing.

We have done the same indoors with flagstones and it works. It might work with bricks - depends on the bricks, naturally.

 

[MdB]

NHL 3.5?? I thought normal lime mortar was used for pointing. (Not that it probably makes an awful lot of difference.)

 

[Jon Maine]

Well, the performance of putty lime outside is dependant on a fair amount of looking after and it does not like extremes of weather, hydraulic will perform better than a putty lime which has been compromised and is certainly easier to tend up to when set. Bear in mind hydraulic lime is natural hydraulic lime, no cement , hence nhl, wouldnt want to use a 5 though, to strong. 3.5 is still flexible and breathable and fit for purpose.
I know quite a few profesionals both conservators and builders who will use hydraulic out of choice externally due to the failure rate of putty which they have suffered due to unpredictable weather and also expensive precautions etc.
On a like for like basis there is an arguement to use putty, which of course you could add a pozzolan to speed setting time, but if you add then again the more you put in the harder and less breathable the mortar will be.
For most re-pointing works I think NHL 3.5 is an acceptable material.
If time to tend a project is no issue so you can pick ideal weather conditions use putty.

 

[Gervase]

...or if you've got a decent scaffold up so you can screen the work. Fat lime does give a more sympathetic result, and certainly makes a richer, stickier mortar, but it does need a bit more TLC. Personally I'd rather use an NHL2 if I couldn't use fat lime, but it depends upon how exposed you are, I suppose.
This was a place I repointed some 18 months ago, and the mortar has cured beautifully, thanks to being screened for the first couple of weeks:

 

[biffvernon]

So how did they manage in ye olden days? There wasn't a lot of NHL 2 or 3.5 around, though a lot of London lime may have been around 1-ish.

 

[Lime]

I would suggest to maintain the colour of the work now and the work to be done in the future that a large enough quantity of sand be bought for both jobs.
Then, as long as the same quality lime is used and in the same proportion, the colour will weather down the same.

 

[Jon Maine]

Come autumn they stopped building and covered the tops of the walls with straw for the winter months. Cant tell you about excessive heat and how they dealt with that. Very likely too a lot of the mortars contained earth and clays which could well have acted as a pozzolan, certainly the current tradition of washed sands is recent.

And of course no shortage of cheap labour who were well versed in the materials they used, unlike today where knowledge is limited, labour expensive and what should be well know building processes have had to be re learnt, best guessing sometimes I am sure.

 

[biffvernon]

Very likely too a lot of the mortars contained earth and clays which could well have acted as a pozzolan, certainly the current tradition of washed sands is recent.

There may be much in that. The limework I've done round about my house has all been with sand dug up on site and I've often deliberately added earth. From a mechanical point of view, I guess you get greater strength if there is a full gradation of grain sizes from coarse, through silts to clays. That almost gives a strong mortar by itself (earth mortar) and the lime can form a matrix that binds everything together without relying on the strength of large calcite crystals. (They are not very strong.) That's before any pozzolanic effect comes into play.

My advice is don't buy washed sand and if you really can't find dirty sand add your own dirt.

 

[skier-hughes]

Hi all,

I have got to re-point the front garden wall. It is only 5-6 bricks high so not a big job.

At some point in the future I am going to re-instate a brick pillar/pier at the end of this wall but will be using a suitable style modern brick as I just cannot afford re-claimed.

Right, over to you chaps and chapesses.

Sam

Sam, have you checked the price of relaimed bricks?

With such a small pier to build, I've bought brics from 40-85p each depending on type.

 

[thiambal]

Right,

As far as me being a cack-handed fool it looks like practice and technique is the answer there.

As for Lime I am more confused than before 2 - 3.5 - 5, hydraulic, non-hydrated, hydrated. aaarrrggh!!!

B&Q sell bags of Blue Circle Hydralime (Hydrated Lime). Is this the stuff I want?

As for colouring, getting the right colour sand makes sense. How about these dye powders you can get?

Sam

 

[Lime]

Using lime will cause the mortar to be stark white.
Only time will dull it down.
Using a colour will make some change but if you think it is easy to get a consistent colour over months or years of making up the mortar mix, think again.

 

[Ian Bond]

Don't add colourants to the mortar, but do try and find an appropriately coloured sand.

If you brush up the pointing after the initial set, you'll bring the aggregate to the surface and lessen the whiteness of the mortar. It will also give the mortar a pleasing texture, rather than a smooth, cement like finish.

Timing is critical - too early with the brushing and you'll smear mortar all over the face of the bricks - too late and the mortar will be too hard for brushing.

How long this takes depends on a number of factors, just as you find with plastering etc. I try and mark the mortar with my thumb nail to test it. If my nail can mark the mortar, but I can't press my thumb into it, I have a go with the brush. If the mortar's still too wet and starts smearing I stop and wait a bit longer.

Personally, I'd stick with a non-hydraulic lime putty unless you are working on something exposed to very harsh weather, say a chimney stack. Then I'd consider using a hydraulic lime, but not a very strong one. You don't want to use a mortar that's harder than the brick or masonry.

I've used bagged hydrated (non hydraulic) lime before to make lime putty, but usually save myself the bother nowadays and buy the putty in tubs.

 

[Nemesis]

I know it's down to personal taste, but we like rubbing back with the pointing trowel. It prevents the smearing. It's the method recommended by Marianne Suhr too.

 

[skier-hughes]

You don't want to use a mortar that's harder than the brick or masonry.

I know this is the recommendation these days, but having taken out a dozen bricks from my house, the lime mortar used is much stronger than the bricks they made. (17th Century)

 

[jason.p]

I know it's down to personal taste, but we like rubbing back with the pointing trowel. It prevents the smearing. It's the method recommended by Marianne Suhr too.

I much prefer a brush, the stiffness of which depends on the degree of set. We usually use 3.5 with a good graded aggregate from say 5mm down, and this can usually be brushed back the following day. (Have to watch it at weekends!). A cut back paintbrush seems to work a well as anything. To my mind the brushing has several functions (I'm talking about stonework). It gets rid of marks left by the pointing iron (I like to use a cut down small plastering tool ). It helps push the mortar into any small cracks, and by exposing the larger bits of aggregate, gives it that natural "weathered" appearance.
As has been mentioned, like any lime work, the aftercare is the trickiest bit of the job, controlling the drying is very important. It may well need spraying and/or covering up maybe for several days in dry weather, or in exposed situations.

 

[Nemesis]

Ah - I'm talking about non-hydraulic.

It works well for that.

 

[thiambal]

Righty ho, I think I had a basic understanding of the technique. Now sorry to sound dim but. What is the difference between NHL 3.5, NHL 5 etc and Can I just use the Blue Circle Hydralime (Hydrated Lime) from B&Q?

This stuff

http://www.diy.com/diy/jsp/bq/nav/nav.jsp?action=detail&fh_secondid=9273115&fh_view_size=6&fh_location=%2f%2fcatalog01%2fen_GB&fh_search=lime&fh_eds=%c3%9f&fh_refview=search&ts=1209927944765&isSearch=true

Although it says on the blue circle website that this is not suitable for use without cement because it is non-hydraulic. To be honest I am not entirely clear of what this all means.

 

[Ian Bond]

The instructions on the bag have to be written for the majority of modern users, but you can safely ignore them and forget the cement.

Or save yourself the bother and buy a tub of ready made lime putty.